Fluorescence sensors that determine the concentration of analytes using the characteristics of the fluorescence that the fluorescence intensity varies depending on the interaction between the analyte and a marker substance are known. For example, an apparatus that determines the concentration of glucose while the whole or a part of the apparatus is embedded in the body of the test subject has been proposed.
Japanese PCT National Publication No. 2007-513333 describes a device in which an optical conduit (for example, a bifurcated fiber bundle) is provided in a puncture needle and a sensing element (for example, a fluorescence unit) is attached to the periphery of the distal end of the optical conduit. Japanese PCT National Publication No. 2007-513333 describes that excitation light is transmitted from the first fiber of the bifurcated fiber bundle and fluorescence is transmitted from the second fiber.
Such a type of fluorescence sensors has the design constraint that the sensing unit needs to be placed in or near the needle tip. Thus, it is necessary to increase the usage efficiency of the excitation light and the fluorescence while minimizing the size of the fluorescence unit. However, Japanese PCT National Publication No. 2007-513333 merely describes a schematic exemplary design and does not describe a specific configuration to increase the usage efficiency of the excitation light and the fluorescence.